Alternator with 6 magnets, 9 coils

[elt]

I think I see it now: I have some wire and a good amount of vinyl ester left over from my first alternator... I'm going to have to build another one. (And I'm not going to ask if this cycle ever ends!) What I'd like to do is make an alternator that will cost less than the $200 45 watt Harbor Freight solar panels. To do that, I need to stretch the magnet budget some; googling, it looks like an overlapping coil design can make do with half the magnets; the downside is that the stator needs to be thicker -

When I searched the site I saw that overlapping coils are usually shown laid down at an angle on the previous one. That makes the stator 3x the thickness of an individual coil.

Can't they just be laid down on top of each other (like I show at the bottom of the drawing.)

I can see that in the "angled" case the that the coil (in effect) moves up an down in the gap as the magnets rotate but that each of the three coils in a leg are getting the same flux at the same time.

In see that in the "flat" coil case that flux in one of the coil in a leg will be slightly different as it will be a little closer (and alternatively slightly farther away) from the magnet pole than the other two coils would be. But won't the voltages in each still add up?

I like the idea of laying out the "flat" coils because I've seen how a narrower gap makes a huge difference in the power generated... I just don't know if it's a bonehead idea or not!

Thank you very much,

 - Ed.

[Nando]

The over-lapping is good for regular motors and generators

The flat insertion is good for an Axial generator.

In both cases the coils see the same level of flux.

Nando

[RP]

If you make the coils oval or rectangular then the overlap only needs to be on the inside or outside diameter sides.  The actual magnet area can be only one winding thick but it'll be a challenge on the inside diameter part to get everything to fit between the magnet circle and the bearing hub.

[windstuffnow]

  The 6/9 combination works well as a single layer as well.  I've only built a small one but it does quite well.

.

[tecker]

This rectangular form for the coils allows for the best right angle alignment to the mags moving in a circle.

[tecker]

I mean triangle duh

[electrondady1]

ed i noticed you are using some tight spaceing on the mags .

is it about 50 % of mag width?

what sort of relationship is there between magnet thickness and the inner spaceing of the magnets.

this is the first time i've seen this combow .

i think i need to build a little grapic model to figure out what is happening.

[windstuffnow]

  It's basically the same as a 12/9 with only 1/2 the magnets.  The coils are slightly smaller than the magnets which I'm sure causes some canceling.  Still, it does a pretty nice job for a quickie air core.  The best I've seen from it was around 4 amps... no idea of the wind speed.  I was playing around with a set of the ABS blades I have and it just fell together on a 6 inch disc.   The coils are simply wired to the wood through some drill holes.  

.

[finnsawyer]

Before you commit to this design take a look at my diary on an alternate alternator design using a 3:2 ratio of coils to magnets.  It fits in exactly with what you are trying to do.  More output with fewer magnets.  Larger rotor, no overlapping of coils.

[elt]

I can't build it if I don't understand it... While I didn't say, I'd like to build a smaller alternator, not a larger one. As you point out, yours has a larger rotor. It looks to me that if I squeeze your design down, say, so that the coils are about the size of the magnets on their inside dimension and make the rotor smaller until the coils touch at their OD's then the alternator is no different than winstuff ed's... I don't see how making the rotor and coils bigger makes anything better. I appreciate that you've written a lot about it but it just doesn't click with me. Maybe someday when someone builds one they'll be able to describe the advantages in words that I can understand.

Thank you,

- Ed.

[finnsawyer]

What is the point of building a smaller alternator if you are going to get less power output?  Why less?  Well to begin with, as I believe someone pointed out, by overlapping the coils you need a stator three times as thick.  Since the flux in a magnetic circuit is determined mostly by the air gap you now get one third the flux.  Leakage flux will also be greater.  With a smaller rotor the magnets will move more slowly past the coils.  This results in a smaller kick or lower voltage.  So does the lower value of flux.  If you don't understand these concepts you probably shouldn't be wasting your money building alternators.

As I understood your original post you had a certain amount of wire and wanted to minimize the cost of magnets for the greatest output.  Well, to maximize output maximize flux and maximize the speed of the magnets past the coils.  The only added cost you would have with my design is the larger rotor.  If you decide to build my design you will have the satisfaction of trying something new that really rocks or else blowing me out of the water (as some people would like to see happen).  Personally, I don't care whether you build it or not, but why do the same old same old especially when you know it isn't going to perform very well?  Or to put it another way, why did you ask for people's opinions if you're not willing to consider other ideas?

[ghurd]

Is the idea for a dual rotor, and there are 12 magnets available?  

Maybe a single rotor with laminations.

Maybe a dual rotor with 1 disk having no magnets.  It seems to be better than laminations.

If the diagram is a single rotor with laminations and overlapping coils, the active area is still only 1 coil thick.

The inner and outer can be thicker and bent over, away from the magnets.  Just like Ed's "alt from scratch".

G-

[elt]

[...] Or to put it another way, why did you ask for people's opinions if you're not willing to consider other ideas?

I think that it's obvious that I considered your opinion ... and decided against it. I appreciate very much that you posted a suggestion and it's not a judgment on the value of your design, only that I'm not going to be the first to build it.

 - Ed.

[finnsawyer]

Actually you will be building it, a folded version.  If the coils move clockwise, or the magnets counterclockwise, the red phase coils will be moving off of a south pole giving a voltage of one polarity.  At the same time the coils of the black phase will be moving onto a north pole and off of a south pole giving the same polarity voltage.  The coils of the blue phase, on the other hand will be producing nearly zero voltage.  So, if you connect the three phases in series you will get a non zero voltage at that time.  Of course, this sort of thing repeats many times around the cycle with the voltage swinging between positive and negative values.  It appears that any time one tries to build an alternator having a coil to magnet ratio of 3:2 the basic physics applicable to the design I have proposed will surface.  Efficiency will be another matter.  I suggest that in testing your alternator you try connecting the phases in series to see what you get.  Other than that have fun!

[finnsawyer]

I need to post a correction.  The voltage produced by the blue phase will not be zero at the time shown.  It will be sweeping off of a north pole and onto a south pole.  The flux through the coils of the blue phase will go through zero as it changes sign, all the while generating a voltage due to the rate of change.  This voltage will be opposite polarity of that due to the other two phases resulting in a reduction of output voltage when the phases are connected in series.  There may still be a non zero voltage, which could result in problems if the phases are connected in delta.